AUSTIN: MUSICAL RECEPTION 225 



which was interrupted in 19 14, the object of the present work 

 being the determination of its sensibiHty, the law of response, 

 and its general applicability to modem receiving conditions, es- 

 pecially with amplifiers. 



The contact maker used in the experiments (figure i) was an 

 old tone wheel having a steel disk about 28 cm. in diameter and 

 754 teeth (with brushes arranged as described above). With 



Fig. 2. — Diagram showing contact points and telephone current. 



this a contact frequency corresponding to a wave length of 

 10,000 meters is obtained at a speed of approximately 2400 

 R. P. M., the power consumed by the motor being about i/io 

 H. P. In order to reduce disturbances in the telephones, the 

 steel disk was insulated from the motor, and the frame connected 

 to ground. With the motor run from a storage battery no 

 trouble was experienced in keeping a practically constant speed 

 w4th which the European stations could be read for hours at a 

 time without speed adjustment. For unsteady sources of power, 

 a speed regulator is of course required. The telephones em- 

 ployed were Baldwin's of 2000 ohms resistance. Figure i shows 

 the circuits employed with radio frequency amplification. 



Comparisons of the sensibility of the oscillating vacuum tube 

 and tone wheel without amplification were made on Annapolis 

 changing the strength of the signal from 10 audibility to several 

 thousand by inserting resistance in the receiving loop, and also 

 in some experiments by varying the main capacity. The results 

 were as follows : 



(i) The sensibiUty of the tone wheel without amplification 

 varies from 1/6 to 1/3 of the sensibility of the oscillating vacuum 

 tube, depending upon the tone and brush adjustment. 



(2) The law of response between telephone current and radio 

 frequency current is linear as in the oscillating vacuum tube. 



